Cardiac Fibrosis in the Pressure Overloaded Left and Right Ventricle as a Therapeutic Target

Myocardial fibrosis is a remodeling process of the extracellular matrix (ECM) following cardiac stress. "Replacement fibrosis" is a term used to describe wound healing in the acute phase of an injury, such as myocardial infarction. In striking contrast, ECM remodeling following chronic pressure overload insidiously develops over time as "reactive fibrosis" leading to diffuse interstitial and perivascular collagen deposition that continuously perturbs the function of the left (L) or the right ventricle (RV). Examples for pressure-overload conditions resulting in reactive fibrosis in the LV are systemic hypertension or aortic stenosis, whereas pulmonary arterial hypertension (PAH) or congenital heart disease with right sided obstructive lesions such as pulmonary stenosis result in RV reactive fibrosis. In-depth phenotyping of cardiac fibrosis has made it increasingly clear that both forms, replacement and reactive fibrosis co-exist in various etiologies of heart failure. While the role of fibrosis in the pathogenesis of RV heart failure needs further assessment, reactive fibrosis in the LV is a pathological hallmark of adverse cardiac remodeling that is correlated with or potentially might even drive both development and progression of heart failure (HF). Further, LV reactive fibrosis predicts adverse outcome in various myocardial diseases and contributes to arrhythmias. The ability to effectively block pathological ECM remodeling of the LV is therefore an important medical need. At a cellular level, the cardiac fibroblast takes center stage in reactive fibrotic remodeling of the heart. Activation and proliferation of endogenous fibroblast populations are the major source of synthesis, secretion, and deposition of collagens in response to a variety of stimuli. Enzymes residing in the ECM are responsible for collagen maturation and cross-linking. Highly cross-linked type I collagen stiffens the ventricles and predominates over more elastic type III collagen in pressure-overloaded conditions. Research has attempted to identify pro-fibrotic drivers causing fibrotic remodeling. Single key factors such as Transforming Growth Factor β (TGFβ) have been described and subsequently targeted to test their usefulness in inhibiting fibrosis in cultured fibroblasts of the ventricles, and in animal models of cardiac fibrosis. More recently, modulation of phenotypic behaviors like inhibition of proliferating fibroblasts has emerged as a strategy to reduce pathogenic cardiac fibroblast numbers in the heart. Some studies targeting LV reactive fibrosis as outlined above have successfully led to improvements of cardiac structure and function in relevant animal models. For the RV, fibrosis research is needed to better understand the evolution and roles of fibrosis in RV failure. RV fibrosis is seen as an integral part of RV remodeling and presents at varying degrees in patients with PAH and animal models replicating the disease of RV afterload. The extent to which ECM remodeling impacts RV function and thus patient survival is less clear. In this review, we describe differences as well as common characteristics and key players in ECM remodeling of the LV vs. the RV in response to pressure overload. We review pre-clinical studies assessing the effect of anti-fibrotic drug candidates on LV and RV function and their premise for clinical testing. Finally, we discuss the mode of action, safety and efficacy of anti-fibrotic drugs currently tested for the treatment of left HF in clinical trials, which might guide development of new approaches to target right heart failure. We touch upon important considerations and knowledge gaps to be addressed for future clinical testing of anti-fibrotic cardiac therapies.

Protective Effects of Thyroid Hormone Deprivation on Progression of Maladaptive Cardiac Hypertrophy and Heart Failure

Purpose: Thyroid hormones (TH) play a central role for cardiac function. TH influence heart rate and cardiac contractility, and altered thyroid function is associated with increased cardiovascular morbidity and mortality. The precise role of TH in onset and progression of heart failure still requires clarification. Methods: Chronic left ventricular pressure overload was induced in mouse hearts by transverse aortic constriction (TAC). One week after TAC, alteration of TH status was induced and the impact on cardiac disease progression was studied longitudinally over 4 weeks in mice with hypo- or hyperthyroidism and was compared to euthyroid TAC controls. Serial assessment was performed for heart function (2D M-mode echocardiography), heart morphology (weight, fibrosis, and cardiomyocyte cross-sectional area), and molecular changes in heart tissues (TH target gene expression, apoptosis, and mTOR activation) at 2 and 4 weeks. Results: In diseased heart, subsequent TH restriction stopped progression of maladaptive cardiac hypertrophy and improved cardiac function. In contrast and compared to euthyroid TAC controls, increased TH availability after TAC propelled maladaptive cardiac growth and development of heart failure. This was accompanied by a rise in cardiomyocyte apoptosis and mTOR pathway activation. Conclusion: This study shows, for the first time, a protective effect of TH deprivation against progression of pathological cardiac hypertrophy and development of congestive heart failure in mice with left ventricular pressure overload. Whether this also applies to the human situation needs to be determined in clinical studies and would infer a critical re-thinking of management of TH status in patients with hypertensive heart disease.

The Degree of Cardiac Remodelling before Overload Relief Triggers Different Transcriptome and miRome Signatures during Reverse Remodelling (RR)-Molecular Signature Differ with the Extent of RR

This study aims to provide new insights into transcriptome and miRome modifications occurring in cardiac reverse remodelling (RR) upon left ventricle pressure-overload relief in mice. Pressure-overload was established in seven-week-old C57BL/6J-mice by ascending aortic constriction. A debanding (DEB) surgery was performed seven weeks later in half of the banding group (BA). Two weeks later, cardiac function was evaluated through hemodynamics and echocardiography, and the hearts were collected for histology and small/bulk-RNA-sequencing. Pressure-overload relief was confirmed by the normalization of left-ventricle-end-systolic-pressure. DEB animals were separated into two subgroups according to the extent of cardiac remodelling at seven weeks and RR: DEB1 showed an incomplete RR phenotype confirmed by diastolic dysfunction persistence (E/e' ≥ 16 ms) and increased myocardial fibrosis. At the same time, DEB2 exhibited normal diastolic function and fibrosis, presenting a phenotype closer to myocardial recovery. Nevertheless, both subgroups showed the persistence of cardiomyocytes hypertrophy. Notably, the DEB1 subgroup presented a more severe diastolic dysfunction at the moment of debanding than the DEB2, suggesting a different degree of cardiac remodelling. Transcriptomic and miRomic data, as well as their integrated analysis, revealed significant downregulation in metabolic and hypertrophic related pathways in DEB1 when compared to DEB2 group, including fatty acid β-oxidation, mitochondria L-carnitine shuttle, and nuclear factor of activated T-cells pathways. Moreover, extracellular matrix remodelling, glycan metabolism and inflammation-related pathways were up-regulated in DEB1. The presence of a more severe diastolic dysfunction at the moment of pressure overload-relief on top of cardiac hypertrophy was associated with an incomplete RR. Our transcriptomic approach suggests that a cardiac inflammation, fibrosis, and metabolic-related gene expression dysregulation underlies diastolic dysfunction persistence after pressure-overload relief, despite left ventricular mass regression, as echocardiographically confirmed.

[Overexpression of miR-130a-3p attenuates cardiomyocyte hypertrophy]

This study aimed to explore the role of miR-130a-3p in cardiomyocyte hypertrophy and its underlying mechanisms. Pressure-overload induced myocardial hypertrophy mice model was constructed by thoracic aortic constriction (TAC). In vitro, norepinephrine (NE) was used to stimulate neonatal rat cardiomyocytes (NRCMs) and H9c2 rat cardiomyocytes to induce hypertrophic phenotypes. The expression of miR-130a-3p was detected in mice hypertrophic myocardium, hypertrophic NRCMs and H9c2 cells. The mimics and inhibitors of miR-130a-3p were transfected into H9c2 cells to observe the role of miR-130a-3p on the hypertrophic phenotype change of cardiomyocytes separately. Furthermore, whether miR-130a-3p regulated hypertrophic related signaling pathways was explored. The results showed that the expression of miR-130a-3p was significantly decreased in hypertrophic myocardium, hypertrophic NRCMs and H9c2 cells. After transfection of miR-130a-3p mimics, the expression of hypertrophic marker genes, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC), and the cell surface area were notably down-regulated compared with the control group (mimics N.C. + NE group). But after transfection of miR-130a-3p inhibitor, the expression of ANP, BNP and β-MHC in H9c2 cells increased significantly, and the cell area increased further. By Western blot, it was found that the protein phosphorylation level of Akt and mTOR were down-regulated after over-expression of miR-130a-3p. These results suggest that miR-130a-3p mimics may alleviate the degree of cardiomyocyte hypertrophy, meanwhile its inhibitor can further aggravate cardiomyocyte hypertrophy. Over-expression of miR-130a-3p may attenuate cardiomyocytes hypertrophy by affecting the Akt pathway.

Modeling heart failure risk in diabetes and kidney disease: limitations and potential applications of transverse aortic constriction in high-fat-fed mice

There is an increased incidence of heart failure in individuals with diabetes mellitus (DM). The coexistence of kidney disease in DM exacerbates the cardiovascular prognosis. Researchers have attempted to combine the critical features of heart failure, using transverse aortic constriction, with DM in mice, but variable findings have been reported. Furthermore, kidney outcomes have not been assessed in this setting; thus its utility as a model of heart failure in DM and kidney disease is unknown. We generated a mouse model of obesity, hyperglycemia, and mild kidney pathology by feeding male C57BL/6J mice a high-fat diet (HFD). Cardiac pressure overload was surgically induced using transverse aortic constriction (TAC). Normal diet (ND) and sham controls were included. Heart failure risk factors were evident at 8-wk post-TAC, including increased left ventricular mass (+49% in ND and +35% in HFD), cardiomyocyte hypertrophy (+40% in ND and +28% in HFD), and interstitial and perivascular fibrosis (Masson's trichrome and picrosirius red positivity). High-fat feeding did not exacerbate the TAC-induced cardiac outcomes. At 11 wk post-TAC in a separate mouse cohort, echocardiography revealed reduced left ventricular size and increased left ventricular wall thickness, the latter being evident in ND mice only. Systolic function was preserved in the TAC mice and was similar between ND and HFD. Thus combined high-fat feeding and TAC in mice did not model the increased incidence of heart failure in DM patients. This model, however, may mimic the better cardiovascular prognosis seen in overweight and obese heart failure patients.

CARD9 as a potential target in cardiovascular disease

Systemic inflammation and localized macrophage infiltration have been implicated in cardiovascular pathologies, including coronary artery disease, carotid atherosclerosis, heart failure, obesity-associated heart dysfunction, and cardiac fibrosis. Inflammation induces macrophage infiltration and activation and release of cytokines and chemokines, causing tissue dysfunction by instigating a positive feedback loop that further propagates inflammation. Cytosolic adaptor caspase recruitment domain family, member 9 (CARD9) is a protein expressed primarily by dendritic cells, neutrophils, and macrophages, in which it mediates cytokine secretion. The purpose of this review is to highlight the role of CARD9 as a potential target in inflammation-related cardiovascular pathologies.

Exercise preconditioning attenuates pressure overload-induced pathological cardiac hypertrophy

Pathological cardiac hypertrophy, a common response of the heart to a variety of cardiovascular diseases, is typically associated with myocytes remodeling and fibrotic replacement, cardiac dysfunction. Exercise preconditioning (EP) increases the myocardial mechanical load and enhances tolerance of cardiac ischemia-reperfusion injury (IRI), however, is less reported in pathological cardiac hypertrophy. To determine the effect of EP in pathological cardiac hypertrophy, Male 10-wk-old Sprague-Dawley rats (n=30) were subjected to 4 weeks of EP followed by 4-8 weeks of pressure overload (transverse aortic constriction, TAC) to induce pathological remodeling. TAC in untrained controls (n=30) led to pathological cardiac hypertrophy, depressed systolic function. We observed that left ventricular wall thickness in end diastole, heart size, heart weight-to-body weight ratio, heart weight-to-tibia length ratio, cross-sectional area of cardiomyocytes and the reactivation of fetal genes (atrial natriuretic peptide and brain natriuretic peptide) were markedly increased, meanwhile left ventricular internal dimension at end-diastole, systolic function were significantly decreased by TAC at 4 wks after operation (P < 0.01), all of which were effectively inhibited by EP treatment (P < 0.05), but the differences of these parameters were decreased at 8 wks after operation. Furthermore, EP treatment inhibited degradation of IκBα, and decreased NF-κB p65 subunit levels in the nuclear fraction, and then reduced IL2 levels in the myocardium of rats subject to TAC. EP can effectively attenuate pathological cardiac hypertrophic responses induced by TAC possibly through inhibition of degradation of IκB and blockade of the NF-κB signaling pathway in the early stage of pathological cardiac hypertrophy.

Bi-modal dose-dependent cardiac response to tetrahydrobiopterin in pressure-overload induced hypertrophy and heart failure

The exogenous administration of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase (NOS), has been shown to reduce left ventricular hypertrophy, fibrosis, and cardiac dysfunction in mice with pre-established heart disease induced by pressure-overload. In this setting, BH4 re-coupled endothelial NOS (eNOS), with subsequent reduction of NOS-dependent oxidative stress and reversal of maladaptive remodeling. However, recent studies suggest the effective BH4 dosing may be narrower than previously thought, potentially due to its oxidation upon oral consumption. Accordingly, we assessed the dose response of daily oral synthetic sapropterin dihydrochloride (6-R-l-erythro-5,6,7,8-tetrahydrobiopterin, 6R-BH4) on pre-established pressure-overload cardiac disease. Mice (n=64) were administered 0-400mg/kg/d BH4 by ingesting small pre-made pellets (consumed over 15-30 min). In a dose range of 36-200mg/kg/d, 6R-BH4 suppressed cardiac chamber remodeling, hypertrophy, fibrosis, and oxidative stress with pressure-overload. However, at both lower and higher doses, BH4 had less or no ameliorative effects. The effective doses correlated with a higher myocardial BH4/BH2 ratio. However, BH2 rose linearly with dose, and at the 400mg/kg/d, this lowered the BH4/BH2 ratio back toward control. These results expose a potential limitation for the clinical use of BH4, as variability of cellular redox and perhaps heart disease could produce a variable therapeutic window among individuals. This article is part of a special issue entitled ''Key Signaling Molecules in Hypertrophy and Heart Failure.''

Lack of beta3 integrin signaling contributes to calpain-mediated myocardial cell loss in pressure-overloaded myocardium

Although cardiac hypertrophy initially ensues as a compensatory mechanism, it often culminates in congestive heart failure. Based on our earlier studies that calpain and beta3 integrin play cell death and survival roles, respectively, during pressure-overload (PO) hypertrophy, we investigated if the loss of beta3 integrin signaling is a potential mechanism for calpain-mediated cardiomyocyte death during PO. beta3 Integrin knockout (beta3) and wild-type mice were used to induce either moderate or severe PO in vivo for short-term (72-hour) and long-term (4-week) transverse aortic constriction. Whereas wild-type mice showed no changes during moderate PO at both time points, beta3 mice exhibited both enrichment of the mu-calpain isoform and programmed cell death of cardiomyocytes after 4-week PO. However, with severe PO that caused increased mortality in both mice groups, cell death was observed in wild-type mice also. To study calpain's role, calpeptin, a specific inhibitor of calpain, was administered through an osmotic mini-pump at 2.5 mg/kg per day beginning 3 days before moderate transverse aortic constriction or sham surgery. Calpeptin administration blocked both calpain enrichment and myocardial cell death in the 4-week PO beta3 mice. Because beta3 integrin contributes to cardioprotective signaling, these studies indicate that the loss of specific integrin function could be a key mechanism for calpain-mediated programmed cell death of cardiomyocytes in PO myocardium.

Adverse ventricular remodeling and exacerbated NOS uncoupling from pressure-overload in mice lacking the beta3-adrenoreceptor

Stimulation of the beta-adrenergic system is important in the pathological response to sustained cardiac stress, forming the rationale for the use of beta-blockers in heart failure. The beta3-adrenoreceptor (AR) is thought to couple to the inhibitory G-protein, G(i), with downstream signaling through nitric oxide, although its role in the heart remains controversial. In this study, we tested whether lack of beta3-AR influences the myocardial response to pressure-overload. Baseline echocardiography in mice lacking beta3-AR (beta3(-/-)) compared to wild type (WT) showed mild LV hypertrophy at 8 weeks that worsened as they aged. beta3(-/-) mice had much greater mortality after transverse aortic constriction (TAC) than WT controls. By 3 weeks of TAC, systolic function was worse. After 9 weeks of TAC, beta3(-/-) mice also had greater LV dilation, myocyte hypertrophy and enhanced fibrosis. NOS activity declined in beta3(-/-)TAC hearts after 9 weeks, and total and NOS-dependent superoxide rose, indicating heightened oxidative stress and NOS uncoupling. The level of eNOS phosphorylation in beta3(-/-)TAC hearts was diminished, and nNOS and iNOS expression levels were increased. GTP cyclohydrolase-1 expression was reduced, although total BH4 levels were not depleted. 3 weeks of BH4 treatment rescued beta3(-/-) mice from worsened remodeling after TAC, and lowered NOS-dependent superoxide. Thus, lack of beta3-AR signaling exacerbates cardiac pressure-overload induced remodeling and enhances NOS uncoupling and consequent oxidant stress, all of which can be rescued with exogenous BH4. These data suggest a cardioprotective role for the beta3-AR in modulating oxidative stress and adverse remodeling in the failing heart.

Sildenafil stops progressive chamber, cellular, and molecular remodeling and improves calcium handling and function in hearts with pre-existing advanced hypertrophy caused by pressure overload

OBJECTIVE

This study sought to test the efficacy of phosphodiesterase type 5A (PDE5A) inhibition for treating advanced hypertrophy/remodeling caused by pressure overload, and to elucidate cellular and molecular mechanisms for this response.

BACKGROUND

Sildenafil (SIL) inhibits cyclic guanosine monophosphate-specific PDE5A and can blunt the evolution of cardiac hypertrophy and dysfunction in mice subjected to pressure overload. Whether and how it ameliorates more established advanced disease and dysfunction is unknown.

METHODS

Mice were subjected to transverse aortic constriction (TAC) for 3 weeks to establish hypertrophy/dilation, and subsequently treated with SIL (100 mg/kg/day) or placebo for 6 weeks of additional TAC.

RESULTS

The SIL arrested further progressive chamber dilation, dysfunction, fibrosis, and molecular remodeling, increasing myocardial protein kinase G activity. Isolated myocytes from TAC-SIL hearts showed greater sarcomere shortening and relaxation, and enhanced Ca(2+) transients and decay compared with nontreated TAC hearts. The SIL treatment restored gene and protein expression of sarcoplasmic reticulum Ca(2+) uptake adenosine triphosphatase (SERCA2a), phospholamban (PLB), and increased PLB phosphorylation (S16), consistent with improved calcium handling. The phosphatase calcineurin (Cn) and/or protein kinase C-alpha (PKCalpha) can both lower phosphorylated phospholamban and depress myocyte calcium cycling. The Cn expression and PKCalpha activation (outer membrane translocation) were enhanced by chronic TAC and reduced by SIL treatment. Expression of PKCdelta and PKCepsilon also increased with TAC but were unaltered by SIL treatment.

CONCLUSIONS

SIL treatment applied to well-established hypertrophic cardiac disease can prevent further cardiac and myocyte dysfunction and progressive remodeling. This is associated with improved calcium cycling, and reduction of Cn and PKCalpha activation may be important to this improvement.

STAT3 activation in pressure-overloaded feline myocardium: role for integrins and the tyrosine kinase BMX

Growth, survival and cytoskeletal rearrangement of cardiomyocytes are critical for cardiac hypertrophy. Signal transducer and activator of transcription-3 (STAT3) activation is an important cardioprotective factor associated with cardiac hypertrophy. Although STAT3 activation has been reported via signaling through Janus Kinase 2 (JAK2) in several cardiac models of hypertrophy, the importance of other nonreceptor tyrosine kinases (NTKs) has not been explored. Utilizing an in vivo feline right ventricular pressure-overload (RVPO) model of hypertrophy, we demonstrate that in 48 h pressure-overload (PO) myocardium, STAT3 becomes phosphorylated and redistributed to detergent-insoluble fractions with no accompanying JAK2 activation. PO also caused increased levels of phosphorylated STAT3 in both cytoplasmic and nuclear fractions. To investigate the role of other NTKs, we used our established in vitro cell culture model of hypertrophy where adult feline cardiomyocytes are embedded three-dimensionally (3D) in type-I collagen and stimulated with an integrin binding peptide containing an Arg-Gly-Asp (RGD) motif that we have previously shown to recapitulate the focal adhesion complex (FAC) formation of 48 h RVPO. RGD stimulation of adult cardiomyocytes in vitro caused both STAT3 redistribution and activation that were accompanied by the activation and redistribution of c-Src and the TEC family kinase, BMX, but not JAK2. However, infection with dominant negative c-Src adenovirus was unable to block RGD-stimulated changes on either STAT3 or BMX. Further analysis in vivo in 48 h PO myocardium showed the presence of both STAT3 and BMX in the detergent-insoluble fraction with their complex formation and phosphorylation. Therefore, these studies indicate a novel mechanism of BMX-mediated STAT3 activation within a PO model of cardiac hypertrophy that might contribute to cardiomyocyte growth and survival.